A mixed-flow pump and an axial-flow pump have been known as conventional pumps. Each of the mixed-flow pump and the axial-flow pump includes an impeller that sends out fluid in a rotation-axial direction, and a diffuser provided downstream of the impeller (see, for example, Patent Document 1).
As the mixed-flow pump, a type of pump having an appropriate performance characteristic suitable for an installation environment is used so that the mixed-flow pump can be efficiently operated according to its installing location or the use for the pump. In this case, if an inlet angle of each of diffuser vanes provided in the diffuser is set to a desired inlet angle, the performance characteristic of the mixed-flow pump can be set to a desired performance characteristic. At this time, the performance characteristic of the mixed-flow pump can be set by changing a bending curvature of each of the diffuser vanes and setting the inlet angle of the diffuser vanes. However, because the bending curvature of the diffuser vane is largely changed, the optimal shape thereof is changed, and there is a concern that a performance of the mixed-flow pump can be deteriorated. To suppress the deterioration in performance of the mixed-flow pump, it is necessary to newly design the shape of the diffuser vane according to a set inlet angle of the diffuser vane. That is, when a desired performance characteristic of the mixed-flow pump is set, it is necessary to newly design each of the diffuser vanes.    Patent Document 1: Japanese Patent Application Laid-open No. 2001-355592